1. (Industrial useful field)
This invention relates to an improvement in a parking device for an automatic transmission suitable for a commercial vehicle in which a torque converter is combined with a transmission.
2. (Prior art and its problem)
In such a conventional parking device, as shown in FIG. 4, a parking gear 102 fastened integrally to an output shaft 100 of a transmission is locked by a locking arm 104 (parking pole) so as to prevent the output shaft 100 from rotating at the time of parking.
The locking arm 104 is so constructed as to be pushed up by a cam 108 of a push rod 106 interlocked with a select lever in a driver's seat to mesh with the parking gear 102, in such a manner as accompanied by a time lag function produced by a coil spring 100, i.e. a function that the cam 108 is elastically pushed by the coil spring 110 when a projection of the locking arm 104 strikes against a top portion of the parking gear 102 and the projection of the locking arm 104 is meshed with its bottom portion after the parking gear 102 revolves.
Further, the locking arm 104 is held to a housing of the transmission through a shaft 112 and a return spring 114, which urges the locking arm 104 apart from the parking gear 102 when a driving range other than P-range (parking range) is selected, is wound around the shaft 112.
However, in a weighty commercial vehicle such as a truck, the locking arm 104 itself is constructed rigidly so that a mass of the locking arm increases and, in addition, a spring of suspension for such truck becomes hard to cause a large vibration to be transmitted to the vehicle. Therefore, the locking arm 104 jumps up against a spring force of the return spring 114 and strikes against said parking gear 102 undesirably.
Moreover, when the spring force of the return spring 114 is stiffened unnecessarily, a force for controlling the push rod 106 is increased uselessly to worsen a driver's feeling of shifting operation.
3. (Object of the Invention)
An object of the present invention is to provide a parking device for an automatic transmission, in which (1) an operating force of a manual select lever can be reduced when P-range is selected; (2) a locking arm is securely parted from a parking gear when a driving range other than P-range is selected; (3) a push rod can be positioned easily even when a distance is short between the locking arm and a transmission side lever interlocked with the select lever.